We have discovered that urinary immunoreactive thromboxane B2 (i-TXB2) may be an early indicator of renal allograft rejection. Twelve patients were studied, each over a period of 26 to 90 days. The change in urinary i-TXB2 appeared to be an earlier indicator of kidney allograft rejection than the change in serum B2 microglobulin or serum creatinine. We propose to follow urinary i-TXB2 in a retrospective study of transplant patients in order to determine its sensitivity and specificity. Furthermore we wish to determine the authenticity of the i-TXB2 and its relation to other arachi-donate metabolities. Urine i-TXB2 will be measured in existing urine samples from 40 kidney transplant patients at the Mayo Clinic; the i-TXB2 will be compared to eight other biochemical parameters already measured and analyzed. The long-term goals are to use the urine i-TXB2 as an early indicator of rejection and thereby obtain an early treatment of kidney allograft rejection which may result in improved kidney allograft fuction and survival. Furthermore early treatment may reduce the amount of corticosteroids used, and thereby reduce morbidity and mortality related to its use. Finally any relation discovered between arachidonic acid metabolites including leukotrienes may result in new approaches to treatment of kidney allograft rejection.